Spectroscopic and theoretical investigations on effective and selective complexation between porphyrins and fullerenes

We have tailored some interesting mono- and diporphyrins, viz., 5, 10, 15, 20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (TP), 5, 15-bis(3, 5-dioctylphenyl)-2, 8, 12, 18-tetramethyl-3, 7, 13, 17-tetradodecyl-21H,23H-porphyrin (AP) and 1, 3-bis(10′,20′-diundecyl-21′H,23′H-porphyrin-5′-yl)benzene (DP) as host molecules to study their complexation behavior with C₆₀ and C₇₀. Fluorescence spectroscopic measurements showed that emission of TP, AP and DP in toluene was quenched in the presence of C₆₀ or C₇₀. Large binding constants (K) in the magnitude of 1.5 × 10⁴ dm³ mol⁻¹ have been obtained for the 1:1 complexes of C₇₀ with TP, AP and DP. However, the C₆₀ complexes have exhibited 8.5 times smaller K compared to C₇₀ complexes. Ab initio theoretical calculations give a good support in favor of strong complexation between C₇₀ and porphyrins.